Micromechanical devices are small structures typically fabricated on a semiconductor wafer using techniques such as optical lithography, doping, metal sputtering, oxide deposition, and plasma etching which have been developed for the fabrication of integrated circuits.
Micromirror devices are a type of micromechanical device. Micromirror devices are primarily used in optical display systems. In display systems, the micromirror is a light modulator that uses digital image data to modulate a beam of light by selectively reflecting portions of the beam of light to a display screen. Other types of micromechanical devices include accelerometers, pressure and flow sensors, gears and motors. While some micromechanical devices, such as pressure sensors, flow sensors, and micromirrors have found commercial success, other types have not yet been commercially viable.
Packaging MEOMS and MEMS presents special challenges. In the case of the micromirror device, the package must provide a hermetically, or near-hermetically sealed environment while providing a distortion-free optical path to the surface of the device and a large number of electrical connections to the device. The package must also be robust enough to withstand extreme thermal gradients when the micromirror array is illuminated by a high optical flux beam.
Furthermore, the package must not create particles during the life of the device. Particles generated within the device can enter the moving superstructure of the MEMS device and electrically short circuit portions of the device or mechanically block the movement of the moving parts. Because of the moving parts and the requirement for some devices to maintain an optical path with the device in the package, the package cavity cannot simply be filled with a potting compound.
Ceramic substrates are preferred for micromirror devices because they provide a good barrier against moisture entering the package. Additionally, ceramic substrates are mechanically robust, allowing them to withstand stresses generated by uneven heating that occurs when the micromirror is illuminated. Unfortunately, ceramic substrates generate particles that can destroy the packaged devices. What is needed is a method and system for preventing particle generation by ceramic package substrates.